Update coding style after pycodestyle 2.1.0

In pycodestyle 2.1.0, E305 was introduced, which requires two blank
lines after top level declarations, too.

See https://github.com/PyCQA/pycodestyle/issues/400

See also #10689; thanks @stepshal for first mentioning this issue and
initial patches

devscripts/make_lazy_extractors.py

@@ -59,6 +59,7 @@ def build_lazy_ie(ie, name):
         s += make_valid_template.format(valid_url=ie._make_valid_url())
     return s
 
+
 # find the correct sorting and add the required base classes so that sublcasses
 # can be correctly created
 classes = _ALL_CLASSES[:-1]